What Is Progesterone?

Progesterone is a sex hormone that plays a key role in the menstrual cycle and in pregnancy. It's also responsible for breast development and preparing the body for breastfeeding.

Progesterone keeps a balance with estrogen, the other primary sex hormone in those assigned female at birth. Progesterone also helps to produce testosterone, the primary sex hormone in males.

This article will explore progesterone's functions, cycles, and supplemental forms.

Where It's Made

In males and females, a small amount of progesterone is made in the adrenal glands, which release hormones for a variety of bodily functions.

• In females, progesterone is primarily produced by the corpus luteum, a part of the ovary. The corpus luteum develops from the follicle that releases an egg from the ovary for ovulation.
• In females, progesterone is also made by the placenta, an organ that develops during pregnancy to help support the fetus.
• It's made to a lesser degree by the testes of those assigned male a birth.

Function

Progesterone plays a few different roles, starting with causing breasts to grow at puberty. Its main jobs are preparing the body for pregnancy and supporting a pregnancy if it occurs.

Progesterone is the dominant hormone in the luteal phase, which is the second half of a menstrual cycle. The luteal phase begins after ovulation and continues until the first day of your period.

Breast Development

Beginning at puberty, progesterone stimulates the growth of breast tissue.

During each luteal phase, the breast tissue is stimulated. The increase in progesterone in the luteal phase of the menstrual cycle is thought to be the cause of the breast swelling, pain, and tenderness that often occurs in this phase of the cycle.

Mastalgia (breast pain) due to the swelling is a common symptom of premenstrual syndrome (PMS).

If you become pregnant, progesterone prepares your breasts for milk production and lactation. 

Menstrual Cycle

After ovulation, the corpus luteum ramps up its progesterone production. This continues the work of estrogen in preparing the lining of the uterus so that it can accept a fertilized egg and so the egg can be implanted for pregnancy.

If you do not become pregnant, then your corpus luteum dissolves and your progesterone levels drop, causing the uterine lining to start to break down.

This results in a period and a new menstrual cycle begins.

Pregnancy

If you become pregnant, the corpus luteum continues to produce progesterone until about 10 weeks of pregnancy. At around 10 weeks, the placenta takes over the production of progesterone for the remainder of the pregnancy.

Research suggests that progesterone may have anti-inflammatory activity and influence over the immune system. These functions of progesterone may help protect an early developing pregnancy from miscarriage and prevent later pregnancy loss and preterm labor (i.e., that which occurs before the 37th week of pregnancy).

Associated Conditions

Low progesterone levels are associated with certain issues, such as:

• Absent periods (known as amenorrhea)
• Infertility
• Miscarriage

If you have problems getting pregnant, your healthcare provider can check your progesterone levels with a blood test. Recent studies suggest that progesterone supplements may help prevent miscarriages.

Mood and Energy Levels

Estrogen and progesterone interact with chemicals in your brain to control your mood and your general sense of well-being.

One way progesterone does this is via its metabolite, a compound known as allopregnanolone.

Allopregnanolone works on a particular receptor in your brain called the GABA receptor. It typically has anxiety-busting action and a calming quality similar to the actions of alcohol and other sedative drugs like benzodiazepines.

This can be beneficial and it may make you feel sleepy or a little low energy right before your period. It also contributes to fatigue that's common during the early part of pregnancy.

For some people, the luteal phase rise in progesterone can cause varying degrees of anxiety and agitation. It is thought that this reaction is caused by a disruption in the processing of allopregnanolone.

Progesterone Supplements

Supplemental progesterone that's made from natural or synthetic sources can be prescribed for a variety of reasons ranging from pregnancy support to contraception.

Methods for supplementing progesterone include:

• Tablets that are taken by mouth
• Shots into a muscle, known as intramuscular injections
• Vaginal gels or suppositories (medication inserted into the vagina)

Progesterone is rapidly cleared from the body when given by mouth, which makes it difficult to use progesterone this way, especially if it is needed only in smaller doses.

Micronized progesterone, which is decreased in particle size for longer effect, can be taken in some instances. It may be prescribed as part of a menopausal hormone replacement regime or to restore periods if you stopped getting periods before menopause.

Progestins, medications that have similar properties to progesterone, provide an option that can be effective when taken by mouth.

For Pregnancy After IVF

For some women, it may be necessary to take supplemental progesterone during pregnancy.

If you conceived with the help of in vitro fertilization (IVF), you might not ovulate naturally and your corpus luteum may not produce enough progesterone.

Your healthcare provider may recommend some type of progesterone support either in the form of a vaginal gel or suppository, tablet, or injections until about 10 to 12 weeks of pregnancy.

Supplemental progesterone may also be used during IVF or intrauterine insemination (IUI) to help promote pregnancy.

For Preterm Labor Prevention

If you have a history of preterm delivery and/or preterm premature rupture of membranes in a previous pregnancy, you may be a candidate to use progesterone injections to try to prevent another preterm birth.

These are weekly injections of a specific type of progesterone that usually begin at 16 to 24 weeks and continue through 36 weeks of pregnancy.

For Contraception

Oral medications containing progestins are commonly used as a contraceptive to prevent pregnancy. An increase in progesterone and its properties prevents ovulation.

Different synthetic progestins act on the progesterone hormone receptors in your body.

Progestins are used in all hormone-containing contraceptives including:

• Birth control pills (oral contraceptives)
• Injectable contraceptives
• Implantable contraceptives
• Progestin-containing intrauterine devices (IUDs)

Most of these synthetic progestins are derived from testosterone. 

For Conditions That Cause Excess Estrogen

Progesterone and estrogen act together to prepare the body for pregnancy, and to support many other bodily functions.

In a normal menstrual cycle in which you don't become pregnant, the buildup and shedding of the lining of your uterus are controlled by a balance between estrogen and progesterone.

If you have a condition where you are not ovulating but have excess estrogen—which is the case in polycystic ovary syndrome (PCOS) and occasionally in obesity—your healthcare provider may suggest the use of a progestin to help protect the lining of your uterus and to treat abnormal uterine bleeding.

For Hormone Replacement Therapy

Progestins are also typically used in many hormone replacement options for the management of menopause symptoms. During menopause, the majority of the unpleasant symptoms, such as hot flashes, are caused by a lack of estrogen.

Taking an estrogen replacement alone will effectively treat these symptoms and protect your bones. However, if you still have your uterus, you may need to also use a progestin or progesterone supplement to prevent abnormal growth of your endometrium and to reduce the risk of endometrial cancer.

Summary

Progesterone is a sex hormone that plays crucial roles in the menstrual cycle and all stages of pregnancy. It also plays a role in breast development and preparing for breastfeeding.

In males, progesterone produced by the adrenal glands and testes plays a role in making testosterone.

Progesterone can be supplemented to support a pregnancy if there are certain risks, such as a history of preterm birth.

Progestins, which act similar to progesterone, are commonly used in hormonal contraceptives and hormone replacement therapy during menopause.

A Word From Verywell

Progesterone plays many roles in the body and it may affect your moods and energy levels in different ways. Different types and formulations of supplemental progesterone have many different uses—including helping promote pregnancy and for contraception.

If you have any concerns about your hormone levels, discuss them with your healthcare provider.